If you cannot open OneCare, then I suspect that .Net Framework on your PC may be damaged.
First, try using the cleanup tool -
http://social.microsoft.com/forums/en-US/onecareinstallandactivate/thread/399071e2-49dc-4767-932d-d261e3965943/
See if you can reinstall successfully after using the cleanup tool.
If that doesn't work, try repairing .Net Framework. Note that the latest update for .Net Framework is 3.5, which rolls in all service packs/updates for prior versions. Multiple versions of .Net can exist on your PC, but OneCare needs 2.0 (or 3.0/3.5).
To repair .Net Framework 2.0 on XP:
Open Control Panel
Select Add or Remove Programs
Locate Microsoft .Net Framework 2.0
Select the entry and when the installer launches, select Repair.
Reboot when it completes.
Alternatively, see this KB article:
http://support.microsoft.com/kb/306160
To remove a corrupt .Net Framework install, use this tool:
http://astebner.sts.winisp.net/Tools/dotnetfx_cleanup_tool.zip
The download of .Net Framework 2.0 can be found here:
http://www.microsoft.com/downloads/details.aspx?familyid=0856eacb-4362-4b0d-8edd-aab15c5e04f5&displaylang=en
To repair .Net Framework 2.0 and 3.0 on Vista, see this blog entry:
http://blogs.msdn.com/astebner/archive/2007/03/26/how-to-repair-the-net-framework-2-0-and-3-0-on-windows-vista.aspx
If the above does not resolve the problem with OneCare, please contact support:
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator
